The word “defense” in the context of negotiable instruments comprises all defenses of the obligator. Defenses are divided into three groups according to their power of assertion: 1. Real (can be claimed against any person) defenses, 2. Defense regarding non-binding characteristics of exchange undertaking (which can be used only by the promisor), 3. Personal defenses. Obligator can assert personal defenses, which only arise from direct relationship between them, against claimant; these defenses cannot be asserted against third parties as a result of abstraction principle, apart from the exception concerning intentional action of bearer to detriment of obligator. Authenticity of the signatures on the bill is independent of each other; binding nature of a signature for its signatory does not affect validity of other signatures.